A. Field of the Invention
This invention relates to methods and apparatus for the remote measurement of the salinity of large bodies of water.
B. Cross Reference to Related Application
The invention relates to some extent to the invention disclosed and claimed in my co-pending U.S. Pat. Application, Ser. No. 451,391.
C. Description of Prior Art
It is believed that the method and apparatus most closely related to the present invention is that taught in the aforementioned co-pending application. In that method the solar glitter pattern from a body of water is continuously sensed as the sensor moves across the surface, perhaps at satellite height. Since the light will, to a large degree, be polarized upon reflection from the surface, the light received by the sensor is polarization analyzed along each plane, and the intensity of both vertical and horizontal components is detected. For each intensity reading of the vertical components, the fractional change of intensity over all (or a large fixed number of) previous such readings is calculated. The same is done with the intensity readings of the horizontally polarized components. The ratio of each corresponding set of vertical to horizontal changes is calculated. Depending on the solar zenith angle (i.e., 90.degree. minus the elevation angle from the horizon), these ratios will by comparison with theoretical values, indicate which of the intensity changes have resulted from a change in salinity, as opposed to other factors, such as sea state. For each intensity change determined to result from a salinity change, the actual change in salinity is calculated, using formulae derived from the Fresnel equations.
The apparatus described in my co-pending application comprises sensor means to acquire corresponding intensity values for the horizontally and vertically polarized light from the solar glitter pattern. These values are analyzed by means for calculation in accordance with the above-described method.
While this previous invention is adequate to obtain reliable salinity measurements under a wide range of conditions, it possesses certain inherent limitations. One of these is that in order to obtain data from which salinity changes may be calculated, a large number of horizontal and vertical polarization intensity readings must be compared to determine initially which data indicate salinity changes and which indicate light intensity changes caused by other factors such as sea state. Accordingly, in this previous method a large number of calculations must be made to obtain reliable data from which salinity changes may be calculated.